In Windows XP, we had net send.
The replacement is supposed to be a command line utility called msg.

However when I try to test this using the following command:

11:19:50.94>msg abhi /SERVER:LT2400 Hello

I get this error.

Error 5 getting session names

Some information: I am logged onto two computers on the same network. LT2400 is the computer I am sending a message to. Both are running windows 7 professional 32 bit. abhi is my logon name on both computers.